JPH0580351B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a printed matter inspection device that detects printing defects by in-line comparing pattern information of a printed matter being printed with reference information in a printing machine.

[Conventional technology]

Conventionally, printing defects on printed matter (oil stains, reverse printing,
Scratches, scratches, doubles, uneven density, misregistration,
Inspections for the presence of defects (poor color tone, wrinkles, etc.) were mainly carried out by operators through sampling inspections. However, such sampling inspections are offline and cannot inspect the quality of all printed matter, so printing defects are sometimes overlooked. Therefore, in order to objectively evaluate the quality of all printed matter being printed, we use strobe lighting that synchronizes with the printing speed and use mirrors that rotate synchronously at high speed to capture printed matter while it is being printed as a still image. Attempts are being made to evaluate.
However, even in this method, quality inspection depends on the operator's judgment. This was because it was believed that the problem was that the patterns of printed matter were different one by one, and that the inspection items for printed matter had subtle differences that had to rely on the human visual angle.

Furthermore, attempts have been made to automate the inspection of the color patches by printing color patches along with the patterns on the printed matter, thereby allowing the inspection of the printed matter to be carried out on behalf of the user. However, with this method, if a printing defect occurs in the pattern area, it will be overlooked, and it could not be said that the function of the inspection device is fully fulfilled.

In recent years, a system for inspecting printed matter using a line sensor has been proposed, as seen in the "Printed Material Inspection Apparatus" described in Japanese Patent Application No. 57-220515. Since this system can automatically inspect the entire pattern of printed matter in-line, it does not have the above-mentioned drawbacks and can be expected to have excellent effects as an inspection device. This system stores the picture information of printed matter in a standard state in advance as reference information in the reference memory, and during inspection, sequentially compares the picture information taken in from the line sensor with the reference information (difference, secondary difference). When these differences exceed the allowable range, it is determined that a printing defect exists. For this reason, even though the accuracy of the test is determined by the set value of this tolerance range, this system does not describe a method for setting the tolerance value that can be easily set and that enables highly accurate testing. The fact that they are not is a big problem.

For this reason, instead of determining the permissible range univocally, a method that allows the user to freely set the permissible range for each pixel of the pattern of the print, such as the "printed matter inspection device" disclosed in Japanese Patent Application No. 57-63221. is proposed.

However, this method has a major drawback in that it takes a lot of time and effort to set the tolerance range. For example, when detecting the surface of a 543mm x 765mm offset rotary press with a B vertical half-cut using 1mmφ pixels, the tolerance range must be determined one by one for a total of 415,395 pixels and input into memory. , it is completely impossible to use it in actual work.

Additionally, a method has been proposed in which the outline of the pattern is extracted by calculation and a rough tolerance is set for the outline, but this method has the drawback that the calculation for extracting the outline requires a large amount of time. . For example, in the contour extraction process for the above-mentioned B vertical and half-sized image, 8
With a BIT microprocessor, it takes about 10 minutes to several tens of minutes, and without an expensive dedicated array processor or minicomputer, it is currently impossible to achieve this in terms of processing speed.

[Problem that the invention seeks to solve]

The present invention has been made in order to cope with the above-mentioned circumstances, and an object of the present invention is to provide a printed matter inspection device that can easily set the above-mentioned tolerance range and enable highly accurate inspection.

[Means for solving problems]

The printed matter inspection apparatus according to the present invention includes a calculation means for determining the amount of variation in the difference between pattern information for each pixel and reference information in a predetermined number of printed materials, and a method based on the amount of variation for each pixel obtained by the calculation means. and setting means for setting an allowable range of the pixel.

[Effect]

According to the printed matter inspection apparatus according to the present invention, since the tolerance range is determined according to the variation in pattern information in a plurality of printed matter, the tolerance range can be easily set and highly accurate inspection can be performed.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a printed matter inspection apparatus according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the circuit configuration of the first embodiment. FIG. 2 is a schematic diagram showing an example of a printed matter inspection device for an offset rotary printing press.

As shown in FIG. 2, in an offset rotary printing press, a strip-shaped printing paper 3 is supplied from a roll-shaped web 2 to a printing section 1. Printing section 1 prints in 4 colors (ink, indigo, red, yellow).
It is equipped with two printing units and sequentially prints four colors (black, indigo, red, and yellow) on the front and back sides of printing paper 3. After the printing paper 3 has been printed, its pattern information is read by a line sensor 4, and then it is conveyed to a dryer and a folding machine section (not shown). A rotary encoder 5 is attached to the blanket cylinder of the final color printing unit of the printing section 1. The rotary encoder 5 outputs a timing pulse in synchronization with the rotation of the blanket cylinder, and this timing pulse is supplied to the inspection device 6. The line sensor 4 scans the printed matter line by line in a direction perpendicular to the conveying direction and reads pattern information for each pixel of the printed matter.
Consists of CCD line sensor etc. line sensor 4
is also connected to the inspection device 6.

The circuit configuration of the inspection device 6 will be explained with reference to FIG. Timing pulses from rotary encoder 5 are supplied to sampling controller 16 . The sampling controller 16 supplies sampling pulses synchronized with the timing pulses from the rotary encoder 5 to the line sensor 4,
Controls the sampling timing of the line sensor 4. Thereby, the scanning line is positioned along the conveyance direction of the printed material.

The picture information IS outputted from the line sensor 4 for each line is supplied via the A/D converter 7 to the reference value memory 8 and the difference circuit 9 as digital data ID (i, j). The writing and reading addresses (i, j) of the reference value memory 8 are set by the memory controller 1.
5. The reference value memory 8 stores, for each pixel, the pattern information of one sheet that is determined to be a normal printed matter by the operator as reference information. As a result, the reference value memory 8 stores the reference data RF(i,
j) is stored.

In order to find the variation in the pattern information of each printed matter, the output reference information RF (i, j) of the reference value memory 8 is used.
and the output pattern information ID (i, j) of the A/D converter 7 are supplied to the difference circuit 9, and the reference information RF (i, j) and the pattern information ID (i, j) are supplied for each pixel (i, j). ) and the difference signal DS(i,j) is obtained. difference signal DS
(i, j) is supplied to the absolute value conversion circuit 18, and an absolute value difference signal (i, j) is obtained.

The absolute value difference signal (i, j) is sent to a comparator circuit 10,
It is supplied to the discrimination circuit 14 and the tolerance value memory 17.
The write and read addresses of the tolerance value memory 17 are also controlled by the memory controller 15. The output of the allowable value memory 17 is also supplied to the discrimination circuit 14.

In the discrimination circuit 14, for each absolute value difference signal (i, j) for each printed matter, the absolute value difference signal '(i, j) in the tolerance memory 17 and the absolute value value conversion circuit 1
Absolute difference signal (i, j) output from 8
The absolute value difference signal (i, j) output from the absolute value converting circuit 18 is higher than the absolute value difference signal ' in the tolerance memory 17.
Only if it is larger than (i, j), write the absolute value difference signal (i, j) output from the absolute value conversion circuit 18 in correspondence with the address (i, j) of the pixel in question into the tolerance memory 17. . That is, ′(i,
j) will be rewritten to (i, j). By repeating this operation for a predetermined number of prints, the maximum value max (i, j) of the absolute difference signal for each pixel within the predetermined number of prints is stored in the tolerance memory 17.
is stored. The allowable value memory 17 uses a constant M (approximately 1.1 to 10) to multiply the maximum absolute value difference signal max(i, j) by M according to an instruction from the CPU 11 via the memory controller 15, and outputs the allowable value signal AS.
Output as (i, j) (=M max (i, j)). As a result, the tolerance value will be automatically set.

When the inspection starts, this tolerance signal AS(i,
j) and the absolute value difference signal (i, j) output from the absolute value conversion circuit 18 are compared for each pixel in the comparison circuit 10. Comparison result ES of comparison circuit 10
(i, j) is supplied to the CPU 11, and the CPU 11 converts the absolute value difference signal (i, j) into an allowable value signal AS (i,
j) If there is even one pixel larger than that, turn on the alarm 12 to warn of the occurrence of a printing defect.

Here, an alarm may be generated only when the number of abnormal pixels is counted and exceeds a certain value.
The above-mentioned constant M can be set using the operation panel 13 according to the required inspection accuracy. Furthermore, the constant M may be made variable depending on the need by dividing it into blocks as shown in Japanese Patent Application No. 134817/1982, or may be made variable in an interactive manner with the display.

Referring to the flowchart shown in Figure 3,
The operation of the embodiment will be explained. FIG. 3 is a flowchart showing how to determine the permissible value for each pixel.
When the printing press starts operating, the operator visually determines whether the currently printed material is normal or not. If the operator determines that the currently printed material is normal, the operator operates the keys on the operation panel 13 to instruct writing of reference information (step S1). As a result, the reference information is written as shown in step S2. That is, the pattern for each line is output from the line sensor 4 in synchronization with the sampling pulse generated from the sampling controller 16 based on the timing pulse from the rotary encoder 5 attached to the blanket cylinder of the final color printing unit. Information Is is written into reference value memory 8 via A/D converter 7 as reference information RF.

In step S3, the pattern information of one printed matter is input. In step S4, a difference signal DS(i,
j) is required. In step S5, the difference signal DS(i,
The absolute value signal (i, j) of j) is obtained.
In step S6, it is determined whether it is the first sheet after starting the tolerance value setting, and if it is the first sheet, step S8 is executed.
Then, this absolute value difference signal (i, j) is written into the tolerance memory 17 and set as '(i, j). 2
In the case of the first or subsequent sheets, it is determined in step S7 whether this absolute value difference signal (i, j) is larger than the absolute value difference signal '(i, j) in the tolerance memory 17. If (i, j)>'(i, j), this absolute value difference signal (i, j) is determined in step S8.
j) is written to the corresponding address (i, j) of the tolerance value memory 17.

The above process is repeated, and it is determined in step S9 whether a predetermined number of sheets (approximately 20 to 100) has been reached.

If the input of the picture information for the predetermined number of sheets has not been completed, input of the picture information in step S3 is executed again. When the input of the picture information for the predetermined number of sheets is completed, in step S10, the maximum value maxDS(i,j) of the absolute value difference signal in the tolerance value memory 17 is multiplied by the constant M, and the tolerance value signal AS(i,j ) is required.

After this, each time the pattern information of each printed matter is input in step S11, the absolute value signal (i, j) of the difference between the input pattern information and the reference information is
(i, j) is compared with the comparison circuit 10, and the absolute value difference signal (i, j) is the allowable value signal AS (i, j)
If even one pixel is larger, it is determined that a printing defect has occurred, and an alarm 12 is issued to issue a warning.

As explained above, according to the first embodiment, the maximum value of the difference between the pattern information and the reference information in a plurality of printed matter is set as the tolerance range, so the tolerance range is determined according to the variation in the printed matter. Become.
Generally, even if the characteristics of a printed matter are stable to some extent, when observed pixel by pixel, there are variations depending on the conditions of the pixel. For example, there is a large difference in the amount of variation depending on what color it is, what the halftone dot percentage is, and whether it is an edge part or not. However, according to the first embodiment, it is difficult to independently measure each of the light intensity fluctuations of the light source for illuminating the line sensor, the permissible density fluctuations of the printed matter, the synchronization of the printed matter, the electrical noise, etc. Provided is a printed matter inspection device that can collectively compensate for the effects of various variations, easily determine tolerance values for inspection according to the degree of variation specific to each pixel, and enable highly accurate inspection. .

Next, a second embodiment of the invention will be described. The first embodiment uses the pattern information of only one printed sheet as the reference information, but the second embodiment averages the pattern information of multiple sheets (approximately 5 to 20 sheets) for each pixel as the reference information. Use the information obtained. Averaging the pattern information can reduce the effects of subtle density differences and noise in printed matter, making it possible to perform highly accurate inspections. FIG. 4 is a circuit diagram of only the portions of the second embodiment that are different from the first embodiment. That is, the second embodiment differs from the first embodiment only in the configuration near the reference memory 8, and the other parts are the same as the first embodiment. In the second embodiment, picture information is averaged over time by an algorithm using the following recurrence formula.

D _o (i, j) = D _o-1 (i, j) + {V _o (i, j) − D _o-1 (i, j)}/2 ^N ......(1) Here, D _o (i, j) is the nth averaged signal obtained as a result of performing averaging processing on the pattern information of the prints up to the nth print, D _o-1 (i, j) is the average signal obtained up to the (n-1)th print The (n-1)th averaged signal obtained as a result of averaging the image information of the n-th printed matter, V _o (i, j) is the image information of the n-th printed matter, and i, j are the pixel positions. , N is a constant (approximately 1 to 5) indicating the degree of averaging processing.

In the second embodiment, the reference memory 8 stores the (n-1)th averaged signal D _o-1 (i, j) as reference information. Output from line sensor 4 and A/D
The picture information V _o (i, j) of the n-th printed matter converted into digital data via the converter 7 is sent to the difference circuit 9
is supplied to the (+) input terminal of the The (-) input terminal of the differential circuit 9 receives the averaged output signal of the memory 42.
D _o-1 (i, j) is supplied. The output signal of the difference circuit 9 is supplied to the absolute value conversion circuit 18, and
The signal is supplied to the division circuit 42. Therefore, the division circuit 42 is supplied with the V _o (i, j)-D _o-1 (i, j) signal. The division circuit 42 performs the 1/2 ^N operation in equation (1) by shifting the data by N bits. The output of the division circuit 42 {V _o-1 (i,
j)-D _o-1 (i, j)}/2 ^N is supplied to the adder circuit 44. The output averaging signal D _o-1 (i, j) of the memory 42 is also supplied to the adder circuit 44 . As a result, the adder circuit 44 outputs the n-th averaged signal D _o (i, j) expressed by equation (1). This signal is written into the reference memory 8.

In this way, according to the second embodiment, since information obtained by averaging the pattern information of a plurality of images (approximately 2 to 32 images) for each pixel is used as the reference information, highly accurate inspection is possible. .

This invention is not limited to the embodiments described above, and can be modified in various ways. The tolerance signal corresponding to the variation in printed matter is not calculated using the maximum value of the difference between the reference information and the input pattern information, but is calculated using the standard deviation, variance, etc. of the difference between the reference information and the input pattern information. Good too. The tolerance signal may be calculated by software. Further, as the difference signal to be compared with the tolerance signal, instead of a simple first-order difference signal, a second-order difference signal such as that described in Japanese Patent Application No. 172,778/1982 may be used.

Furthermore, in the second embodiment, an arithmetic average or a weighted average may be used instead of the time-series average of the picture information.

〔Effect of the invention〕

As explained above, according to the present invention, the permissible range is determined according to the variation in pattern information in multiple printed materials, so the permissible value during inspection can be easily determined, and highly accurate inspection is possible. It is possible to provide a printed matter inspection device that does the following.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the circuit configuration of the first embodiment, FIG. 2 is a schematic diagram showing an example of a printed matter inspection device in an offset rotary printing press, and FIG. 3 is a flowchart showing the operation of the first embodiment. Figure 4 is the second
FIG. 2 is a block diagram showing the circuit configuration of the main part of the embodiment. 4... Line sensor, 5... Rotary encoder, 8... Reference value memory, 9... Differential circuit, 10
... Comparison circuit, 11 ... CPU, 14 ... Discrimination circuit, 17 ... Tolerance value memory, 18 ... Absolute value conversion circuit.

Claims (1)

[Claims] 1. Detecting pattern information on a printed matter, calculating the difference for each corresponding pixel between the detected pattern information and pre-stored reference information, and determining whether the difference is within an allowable range. In a printed matter inspection apparatus that inspects printed matter for printing defects based on a predetermined number of printed matter, a calculation means for determining the maximum value of the difference between pattern information and reference information for each pixel for a predetermined number of printed matter; 1. A printed matter inspection apparatus, comprising: setting means for setting an allowable range for each pixel by multiplying a value by a constant. 2. The printed matter inspection apparatus according to claim 1, wherein the reference information is an average value of pattern information of a predetermined number of printed matter. 3. Detects the pattern information of the printed material, calculates the difference for each corresponding pixel between the detected pattern information and pre-stored reference information, and prints the printed material based on whether the difference is within an allowable range. A print inspection device for inspecting defects includes a calculation means for calculating the standard deviation of the difference between pattern information and reference information for each pixel of a predetermined number of prints, and a calculation means for multiplying the standard deviation obtained by the calculation means by a constant. 1. A printed matter inspection device, comprising: a setting means for setting an allowable range for each pixel. 4. The printed matter inspection apparatus according to claim 3, wherein the reference information is an average value of pattern information of a predetermined number of printed matter. 5 Detect the pattern information of the printed material, calculate the difference for each corresponding pixel between the detected pattern information and pre-stored reference information, and print the printed material based on whether the difference is within the allowable range. A print inspection device for inspecting defects includes a calculation means for calculating the variance of the difference between pattern information and reference information for each pixel for a predetermined number of prints, and a calculation means for calculating the variance for each pixel by multiplying the variance obtained by the calculation means by a constant. 1. A printed matter inspection device, comprising: a setting means for setting an allowable range. 6. The printed matter inspection apparatus according to claim 5, wherein the reference information is an average value of pattern information of a predetermined number of printed matter.